Method and system for operating and monitoring a well for extracting or storing fluid

ABSTRACT

The system for operating and monitoring a well for extracting or storing an operating fluid, such as natural gas, comprises a production column in which the operating fluid flows, a protective casing arranged around the production column, and a cement sheath interposed between the casing and a rock formation through which the well extends. The system further comprises, outside the casing, between the casing and the cement sheath, a series of electronic units distributed in predetermined positions in a succession of planes perpendicular to the casing and spaced apart axially along the casing. Each electronic unit comprises communication means enabling the electronic unit to communicate with another electronic unit or with a surface terminal, a power supply unit of the electronic unit, and at least one of the following elements: a) a detector unit comprising at least one sensor for sensing a physical or chemical magnitude, and b) a signal processor unit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §365 to InternationalPatent Application No. PCT/FR2015/051469 filed on Jun. 3, 2015, whichclaims priority to French Patent Application No. 1455078 filed on Jun.4, 2014. Both of these applications are hereby incorporated by referencein their entirety.

TECHNICAL FIELD

The present invention relates to a system for operating and monitoring awell for extracting or storing an operating fluid such as natural gas,the well comprising a production column in which the operating fluidflows, protective casing arranged around the production column, and acement sheath interposed between the casing and a rock formation throughthe well extends.

The invention also provides a method of operating and monitoring a wellfor extracting or storing an operating fluid, the monitoring includingtracking the placing and the integrity of the cement protection barrier.

The integrity of a well for extracting or storing a fluid such as ahydrocarbon or natural gas can be affected by the presence of voidswhile cement is being used to fill the annular gap situated between thecasing of the extraction well and the surrounding rock, or indeed as aresult of the cement aging. These two factors can give rise to unwantedstoppages of production, which, by their very nature, are notforeseeable, unless the integrity of the cement sheath is monitoredregularly.

It is therefore desirable to be able to inspect the integrity of thecement sheath in reliable and effective manner in order to be able topredict stoppages of production and act appropriately to minimize thelosses of production associated with stopping operation.

There exist probes and well-logging methods that enable a well to beinspected at a point in time. The state (cracks or voids) of the cementcan thus be observed and poor quality cementing can be identified (i.e.places where the annular space is incompletely filled). A major drawbackof that method is that it is intrusive and requires production to bestopped, since the probe needs to be inserted inside the casing, whichinvolves removing the production column.

Indirect measurements are also known for detecting leaks, such asanalyzing fluids or analyzing pressure outside the well, for example.Nevertheless, such indirect methods serve to confirm a problem but notto anticipate it.

Thus, logging and indirect measurements do not enable cement to betracked over the long term, nor do they enable cementing to be inspectedso as to provide a method that is suitable for anticipating productionstoppages.

Proposals have already been made to disperse sensors in the cementsheath interposed between the casing and the well for extracting orstoring fluid and the rock formation through which the well extends, forthe purposes of inspecting the integrity of the cement sheath and ofmonitoring its aging. Nevertheless, acting in that way does not make itpossible to guarantee that sensors are distributed in uniform mannerwithin the cement sheath. Furthermore, the nanometric size of embeddedsensors, as is required for incorporating the sensors in cement,prevents independent and non-wired sensors being electrically poweredand being able to communicate among one another, as is necessary forthem to operate.

Also known, from Document WO 2011/017415 A2 is a borehole fitted withtemperature sensors and strain gauges distributed along the casingbetween the casing and the cement sheath, which sensors may be placed insuccessive horizontal planes or else arranged following a helical path.

SUMMARY

The present invention seeks to remedy the above-mentioned drawbacks andto make it possible to inspect in reliable and effective manner theproper placing and integrity of the cement sheath situated between acasing and a rock formation, in order to be able to predict stoppages ofproduction in the well for extracting or storing fluid and to actaccordingly in order to minimize production losses associated withstopping operation.

These objects are achieved in accordance with the invention by means ofa system for operating and monitoring an extraction or storage well foran operating fluid such as a hydrocarbon, geothermal water, carbondioxide, or natural gas, the well comprising a production column inwhich said operating fluid flows, a protective casing arranged aroundthe production column via an annulus fluid, and a cement sheathinterposed between the casing and a rock formation through which thewell extends, the system being characterized in that it comprises,outside the casing, between the casing and the cement sheath, a seriesof electronic units distributed in predetermined positions in asuccession of planes perpendicular to the casing and spaced apartaxially along the casing, each electronic unit comprising communicationmeans enabling the electronic unit to communicate with anotherelectronic unit or with a surface terminal, a power supply unit of theelectronic unit, and at least one of the following elements: a) adetector unit comprising at least one sensor for sensing a physical orchemical magnitude, and b) a signal processor unit, and in that at leastone electronic unit is arranged as a relay unit in which thecommunication means include means for receiving signals transmitted bysurrounding electronic units and means for transmitting signals receivedfrom the surrounding electronic units and amplified by a signalprocessor unit.

Each detector unit may comprise a sensor corresponding to measuring asingle type of physical or chemical magnitude.

Nevertheless, in a variant embodiment, each detector unit comprises aset of a plurality of sensors corresponding to measuring a plurality ofdifferent physical or chemical magnitudes.

The independent sensors making it possible to measure a physical orchemical magnitude in the volume of the cement sheath in order toinspect its integrity may in particular comprise ultrasound sensors,radar sensors, and/or terahertz sensors, and additionally temperaturesensors and/or strain gauges.

Depending on the intended application, between one to eight electronicunits are distributed around the casing in a common plane perpendicularto said casing.

In a preferred particular embodiment, the communication means compriseswireless communication means, such as radiowaves, electromagnetic waves,soundwaves, or surface currents.

Radio communication means for returning information by radio frequencyin the cement sheath preferably make use of a frequency lying in therange 169 megahertz (MHz) to 2.4 gigahertz (GHz). This makes it possibleto combine an antenna of reasonable size (of centimeter order) withrange that is sufficient (of the order of about ten meters).

In another possible embodiment, the communication means comprise wiredcommunication means.

The electronic units may be fastened directly on the casing by amechanical connection, such as adhesive, soldering, or welding.

In a particular embodiment, the electronic units are put directly intocontact with the casing, the electronic units and the casing then beingcovered by a protective polymer layer for protecting the electronicunits and the casing and for ensuring that the electronic units are heldon the casing.

In another embodiment, the electronic units are arranged on a continuousstrip that is adhesively bonded on a generator line of the casing andthat is in contact with the cement sheath.

The invention makes it possible to arrange sensors at very preciselocations along the casing.

In an embodiment, a first series of electronic units of a first type arearranged in planes perpendicular to the casing that are spaced apartaxially at a large first mesh, and a second series of electronic unitsof a second are arranged in planes perpendicular to the casing that arespaced apart axially in a smaller second mesh.

By way of example, the electronic units including at least one detectorunit are arranged in planes perpendicular to the casing that are spacedapart axially from one another by 10 centimeters (cm) to 10 meters (m).

The electronic units not including a detector unit may be arranged inplanes perpendicular to the casing that are spaced apart axially fromone another by 5 m to 100 m.

In particular, the invention provides a system in which the detectorunits include at least one sensor selected from sensors of temperature,pressure, strain, or integrity, such as a sensor for sensing density,the presence of material, or the chemical environment, such as thepresence of water or sulfur.

In a particular embodiment, the electronic units have thickness lying inthe range 1 millimeters (mm) to 20 mm.

The power supply unit of each electronic unit comprises electricalenergy storage means, such as a battery or a supercapacitor.

In particular, it is possible to use high temperature batteries, such assolid cathode lithium batteries having a capacity of about 10 watt hours(Wh) to 50 Wh as a function of the data transmission protocol used, orindeed a system of micro fuel cells.

The power supply unit of each electronic unit may equally well comprisemeans for receiving energy, such as electromagnetic energy transmittedalong the casing or mechanical or thermal energy collected by means ofmagneto-inductive, piezoelectric, or Seebeck transducers.

Thus, in a particular embodiment, at least one electronic unit arrangedas a relay unit recovers energy from the surrounding medium in order topower the at least one detector unit comprising at least one sensor forsensing a physical or chemical magnitude and/or the at least one signalprocessor unit. Energy may also be obtained in particular by collectingthermal energy from the well by using the temperature gradient betweenthe surrounding medium and the operating fluid.

The invention also provides a fabrication method for fabricating thecasing of a well for extracting or storing an operating fluid, themethod being characterized in that it comprises the steps consisting in:

providing a set of casing elements;

prior to inserting each casing element in the extraction well, fasteningthereon a series of electronic units distributed in predeterminedpositions in a succession of planes perpendicular to the casing andspaced apart axially along the casing, each electronic unit comprisingcommunication means enabling the electronic unit to communicate withanother electronic unit or with a surface terminal, a power supply unitof the electronic unit, and at least one of the following elements: a) adetector unit comprising at least one sensor for sensing a physical orchemical magnitude, and b) a signal processor unit, at least oneelectronic unit being arranged as a relay unit in which thecommunication means include means for receiving signals transmitted bysurrounding electronic units and means for transmitting signals receivedfrom the surrounding electronic units and transformed by a signalprocessor unit; and

fastening the casing elements together end-to-end to form the casing.

In this method of fabricating the casing of an extraction well, the stepof fastening electronic units on the casing is performed on a generatorline of the casing element by adhesive, soldering, or welding, and theelectronic units are covered by a protective polymer layer.

The invention also provides a method of operating and monitoring a wellfor extracting or storing an operating fluid such as a hydrocarbon,geothermal water, carbon dioxide, or natural gas, the method comprisingthe steps consisting in making a borehole in a geological formation,arranging a protective casing in the borehole, and interposing a sheathof cement between the casing and the geological formation, the methodbeing characterized in that the casing is made in accordance with theabove-defined fabrication method.

BRIEF DESCRIPTION OF THE DRAWING

Other characteristics and advantages of the invention appear from thefollowing description of particular embodiments given as examples, withreference to the accompanying drawing, in which:

FIG. 1 is a diagrammatic vertical section view of a well fitted with anoperating and monitoring system of the invention;

FIG. 2 is a section view on line II-II of FIG. 1; and

FIG. 3 is a block diagram showing the essential components of an exampleof an electronic unit suitable for being used in the operating andmonitoring system of the invention.

DETAILED DESCRIPTION

FIG. 1 shows an example of a well for extracting or storing an operatingfluid such as a hydrocarbon, geothermal water, carbon dioxide, ornatural gas, to which the invention is applicable. FIG. 1 shows avertical well, but the invention is equally applicable to a well that isinclined relative to the vertical.

FIG. 1 shows a production column 20 in which the operating fluid flows,a protective casing 60 arranged around the production column 20 via anannulus fluid 25, and a cement sheath interposed between the casing 60and a rock formation 70 through which the well extends. Outside thecasing 60, between the casing the cement sheath 30, a series ofelectronic units 110 are distributed in predetermined positions in asuccession of planes perpendicular to the casing 60 and spaced apartaxially along the casing 60.

As shown diagrammatically in FIG. 3, each electronic unit 110 comprisesat least communication means 14 enabling the electronic unit 110 tocommunicate with another electronic unit or with a surface terminal 100,and a power supply unit 13 of the electronic unit together with at leastone of the following elements:

a) a detector unit comprising at least one sensor 11 for sensing aphysical or chemical magnitude; and

b) a signal processor unit 12.

An electronic unit 110 having only a detector unit of point a) is thusan independent unit arranged to take measurements of at least onephysical or chemical magnitude and to transmit the taken measurementseither to another electronic unit 110 acting as a relay for themeasurements, or else to a surface terminal 100 that serves to collectand analyze the measurement data that has been measured.

An electronic unit having only a processor unit 12 of point b) is thus arelay arranged to receive data from other electronic units 110, inparticular sensors of a physical or chemical magnitude, and to forwardthe data either to another electronic unit 110 that also acts as arelay, or else to the surface terminal 100. The signal processor unit 12serves to filter and transform signals it receives in order to preservethe quality of the forwarded signal. Such an electronic unit 110 alsoincludes signal receiver means, such as an antenna suitable for thesignal. For greater clarity, the electronic unit 110 suitable forrelaying signals is referred to below as a relay unit.

The electronic units 110 may be arranged to comprise both a detectorunit with a sensor 11 and a signal processor unit 12 in order to combinethe functions of being a relay and of measuring physical or chemicalmagnitudes, as shown in FIG. 3.

Each detector unit may have either a sensor 11 corresponding to a singletype of physical or chemical magnitude, or else a set comprising aplurality of sensors 11 for sensing different physical or chemicalmagnitudes.

FIG. 2 shows an assembly comprising a single electronic unit 110situated in a given horizontal plane perpendicular to the verticalcasing 60, but this number could be different. Thus, in general manner,between one to eight electronic units 110 may be arranged around thecasing 60 in a single plane perpendicular to the casing 60.

The communication means 14 associated with the electronic units 110 maycomprise wireless communication means, e.g. using radiowaves,soundwaves, electromagnetic waves, or surface currents, or in anotherembodiment, they may comprise wired communication means.

Radio communication means for returning information by radio in thecement sheath preferably use a frequency lying in the range 169 MHz to2.4 GHz. This makes it possible to combine an antenna of size that isreasonable (of centimeter order) and a range that is sufficient (of theorder of about ten meters).

The electronic units 110 may be fastened directly to the casing 60 orthey may be arranged on a continuous strip 61 that is adhesively bondedto a generator line of the casing 60 and that is in contact with thecement sheath 30. In a particular embodiment, the sensors are fastenedto a metal belt that is then closed and tightened around the casing 60.

The electronic units 110 may include transmission means 12 adapted totransmit the measurement signals from one to the next towards a base 100situated at the surface of the ground.

The electronic units 110 may be fastened to the casing 60 by adhesive orthey may be fastened to a flexible support surrounding the casing 60.

When the casing 60 is made of steel, the electronic units 110 may alsobe fastened to the casing 60 by welding or soldering.

In a preferred embodiment, the electronic units 110 are put directlyinto contact with the casing 60, the electronic units 110 and the casing60 then being covered by a protective polymer layer 61 for protectingthe electronic units and the casing while bending and conditioning thecasing and during manipulations before and during laying of the casing,and also for holding the electronic units 110 on the casing 60.

The electronic units 110 typically include microcomponents in order toreduce the size of each electronic unit. Thus, the electronic units 110typically present thickness lying in the range 1 mm to 20 mm. Theelectronic units 110 can thus be covered in a protective polymer layer61.

Nevertheless, incorporating certain components, such as a battery forexample, can lead to the electronic units 110 being thicker, e.g. havingthickness up to as much as 50 mm. Under such circumstances, the casing60 should include housings of size and depth corresponding to theelectronic units 110 so that they are embedded in the casing prior toapplying the protective polymer layer 61.

In a configuration that is advantageous, but not exclusive, a firstseries of electronic units 110, each having a detector element 11 fordetecting a first type of physical or chemical magnitude, are arrangedin planes perpendicular to the casing 60 that are spaced apart axiallyat a large first mesh of length L1 and in FIG. 1 they are referenced asbeing the units 111, 112, 115, 116, and 118.

Under such circumstances, a second series of electronic units 110, eachincluding a detector element 11 for detecting a second type of physicalor chemical magnitude, are arranged in planes perpendicular to thecasing 60 that are spaced apart axially at a smaller second mesh oflength L2 over at least a fraction of the height of the casing 60, andthey are referenced in FIG. 1 as being the units 113 and 114 situatedlevel with the formation 40, and the units 116 and 117 situated levelwith the formation 50. It should be observed that units such as the unit116 may be common to both meshes in which case they have detectorelements 11 for detecting both the first and the second types ofphysical or chemical magnitude.

The electronic units 110 may be arranged in planes perpendicular to thecasing 60 that are spaced apart axially from one another, e.g. in therange 10 cm to 100 m, however other ranges of values are possibledepending on the applications.

Advantageously, the electronic units 110 having at least one detectorunit are arranged in planes perpendicular to the casing 60 that arespaced apart axially from one another in the range 10 cm to 10 m inorder to create a sensor mesh suitable for detecting modifications inthe cement sheath 30. In addition, the mesh of sensors 11 may bemodulated depending on the geological layers encountered. Thus, the meshof temperature or pressure sensors may be adapted to the depth of theborehole, with the mesh becoming denser with increasing depth of theborehole.

In similar manner, electronic units 110 that do not have at least onedetector unit, in particular the relay units, are arranged in planesperpendicular to the casing 60 that are spaced apart axially from oneanother by a distance in the range 5 m to 100 m, i.e. at a larger mesh,but suitable for enabling the electronic units 110 to communicate withone another.

More generally, in a preferred embodiment of the invention, each sensor11 has its own mesh, the relay units being arranged so that each sensor11 can send data to the surface terminal 100. Whenever possible, thesensors and/or relays are grouped together in an electronic unit 110 inorder to facilitate implementation.

The detector units comprise at least one sensor 11 selected from sensorsfor sensing the following physical magnitudes: temperature, pressure,strain, and integrity, such as the density or the presence of materialin order to detect missing cement, chemical environment, such as thepresence of water or sulfur, in order to detect infiltration of water orof elements that might affect the casing 60.

By way of example, the electronic units 113, 114 and 116, 117 maycomprise a first series of detector units, each comprising a pressuresensor, and the electronic units 111, 112, 115, 116, and 118 maycomprise a second series of detector units each comprising a temperaturesensor.

Under such circumstances, the electronic units 113, 114 and 116, 117 ofthe first series may be arranged in planes perpendicular to the casing60 that are spaced apart axially from one another by a length L2 lyingin the range 50 cm to 150 cm, and the electronic units 111, 112, 115,116, and 118 of the second series may be arranged in planesperpendicular to the casing 60 that are spaced apart axially from oneanother by a length L1 lying in the range 5 m to 15 m.

According to a particular characteristic, the detector units of theelectronic units 110 are electrically powered by means for receivingenergy, such as electromagnetic energy transmitted along the casing 60.Electrical power supply may also be obtained by collecting mechanicaland thermal energy, e.g. by means of magneto-inductive, piezoelectric,or Seebeck effect transducers.

Thus, in a particular embodiment, at least one electronic unit arrangedas a relay unit recovers energy from the surrounding medium in order topower at least one detector unit having at least one sensor for sensinga physical or chemical magnitude and/or at least one signal processorunit. Energy may also be obtained in particular by collecting thermalenergy from the well and using the temperature gradient between thesurrounding medium and the operating fluid.

In another embodiment, each electronic unit 110 has an independentbattery or electrical power supply capacitors constituting the energysource 13.

The invention also provides a method of fabricating the casing 60 of awell for extracting or storing an operating fluid, the method consistingin:

providing a set of casing elements;

prior to inserting each casing element in the extraction well, fasteningthereon each casing element a series of electronic units 110 distributedin predetermined positions in a succession of planes perpendicular tothe casing 60 and spaced apart axially along the casing 60, eachelectronic unit 110 comprising communication means 14 enabling theelectronic unit 110 to communicate with another electronic unit 110 orwith a surface terminal 100, a power supply unit 13 of the electronicunit 110, and at least one of the following elements: a) a detector unitcomprising at least one sensor 11 for sensing a physical or chemicalmagnitude, and b) a signal processor unit 12; and

fastening the casing elements together end-to-end in order to form thecasing.

The casing elements are tubes, generally made of steel and having alength of 10 m, for example, and they are produced in a factory, withthe complete casing thus being obtained by way of example by screwingthese various elements together end to end. In the invention, thesecasing elements are fitted with electronic units 110 as defined above inthe factory. The casing elements are then assembled while making theextraction well.

More precisely, in a preferred embodiment of the invention, theelectronic units 110 are arranged on the casing 60 by temporaryadhesive. Then the casing 60 and the electronic units 110 are covered bya protective polymer layer 61, which fastens the electronic units 110 onthe casing 60. This layer 61 is selected so as to enable the sensors 11to be used while enabling the electronic units 110 to be fastened to thecasing 60.

The method also includes steps consisting in installing, outside thecasing 60, between the casing and the cement sheath 30, a series ofelectronic units 110, comprising detector units and/or relay units, thatare distributed in predetermined positions in a succession of planesperpendicular to the casing 60 and spaced apart axially along the casing60. Each detector unit comprises at least one sensor 11 for sensing aphysical or chemical magnitude, communication means 14 for signalscoming from the sensor 11, a power supply unit 13, and where appropriatea signal processor unit 12 for processing signals from the sensor 11.Each relay unit comprises signal transmission means 14, a power supplyunit 13, and where appropriate a unit 12 for processing the relayedsignals. FIG. 3 shows an electronic unit 110 combining both thefunctions of a detector unit and the functions of a relay unit.

1. A system for operating and monitoring an extraction or storage wellfor an operating fluid, the well comprising (i) a production column inwhich the operating fluid flows, (ii) a protective casing arrangedaround the production column, and (iii) a cement sheath interposedbetween the casing and a rock formation through which the well extends,the system comprising: outside the casing, between the casing and thecement sheath, a series of electronic units distributed in specifiedpositions in a succession of planes perpendicular to the casing andspaced apart axially along the casing, each electronic unit comprising(i) a communication unit configured to enable the electronic unit tocommunicate with another electronic unit or with a surface terminal,(ii) a power supply, and (iii) at least one of: (a) a detectorcomprising at least one sensor configured to sense a physical orchemical magnitude or (b) a signal processor; wherein at least one ofthe electronic units is configured as a relay in which the communicationunit comprises a receiver configured to receive signals transmitted byone or more surrounding electronic units and a transmitter configured totransmit signals received from the one or more surrounding electronicunits and transformed by the signal processor.
 2. The system accordingto claim 1, wherein each detector comprises a sensor configured tomeasure a single type of physical or chemical magnitude.
 3. The systemaccording to claim 1, wherein each detector comprises a plurality ofsensors configured to measure a plurality of different physical orchemical magnitudes.
 4. The system according to claim 1, wherein one toeight electronic units are distributed around the casing in a commonplane perpendicular to the casing.
 5. The system according to claim 1,wherein the communication unit comprises a wireless radio.
 6. The systemaccording to claim 1, wherein the communication unit comprises a wiredcommunication unit.
 7. The system according to claim 1, wherein theelectronic units are fastened directly on the casing.
 8. The systemaccording to claim 1, further comprising: a protective polymer layerconfigured to protect the electronic units and the casing and configuredto hold the electronic units on the casing.
 9. The system according toclaim 1, wherein the electronic units are arranged on a continuous stripthat is adhesively bonded on a generator line of the casing and that isin contact with the cement sheath.
 10. The system according to claim 1,wherein: a first series of electronic units of a first type is arrangedin planes perpendicular to the casing that are spaced apart axially at alarger first mesh; and a second series of electronic units of a secondtype is arranged in planes perpendicular to the casing that are spacedapart axially at a smaller second mesh.
 11. The system according toclaim 1, wherein the electronic units including the detectors arearranged in planes perpendicular to the casing that are spaced apartaxially from one another by 10 cm to 10 m.
 12. The system according toclaim 1, wherein the electronic units not including the detectors arearranged in planes perpendicular to the casing that are spaced apartaxially from one another by 5 m to 100 m.
 13. The system according toclaim 1, wherein the detectors are configured to detect at least one of:temperature, pressure, strain, integrity, density, a presence ofmaterial, or a chemical environment.
 14. The system according to claim1, wherein the electronic units have a thickness of 1 mm to 20 mm. 15.The system according to claim 1, wherein the power supply of eachelectronic unit comprises a battery or a supercapacitor.
 16. The systemaccording to claim 1, wherein the power supply of each electronic unitis configured to receive electromagnetic energy transmitted along thecasing or mechanical or thermal energy collected by magneto-inductive,piezoelectric, or Seebeck transducers.
 17. The system according to claim1, wherein the at least one electronic unit configured as the relay isconfigured to recover energy from a surrounding medium in order to powerat least one of: the detector or the signal processor.
 18. A method forfabricating a casing of a well for extracting or storing an operatingfluid, the method comprising: providing a set of casing elements; priorto inserting the casing elements in the well, fastening thereon a seriesof electronic units to be distributed in specified positions in asuccession of planes perpendicular to the casing and spaced apartaxially along the casing, each electronic unit comprising (i) acommunication unit configured to enable the electronic unit tocommunicate with another electronic unit or with a surface terminal,(ii) a power supply, and (iii) at least one of: (a) a detectorcomprising at least one sensor configured to sense a physical orchemical magnitude or (b) a signal processor, at least one of theelectronic units configured as a relay in which the communication unitcomprises a receiver configured to receive signals transmitted by one ormore surrounding electronic units and a transmitter configured totransmit signals received from the one or more surrounding electronicunits and transformed by the signal processor; and fastening the casingelements together end-to-end to form the casing.
 19. The methodaccording to claim 18, wherein the electronic units are fastened on agenerator line of the casing elements by adhesive, soldering, orwelding.
 20. The method according to claim 18, wherein the electronicunits are covered by a protective polymer layer.
 21. A method ofoperating and monitoring a well for extracting or storing an operatingfluid, the method comprising: making a borehole in a geologicalformation; arranging a protective casing in the borehole; andinterposing a sheath of cement between the casing and the geologicalformation; wherein the casing is made by: obtaining a set of casingelements; prior to inserting the casing elements in the well, fasteningthereon a series of electronic units to be distributed in specifiedpositions in a succession of planes perpendicular to the casing andspaced apart axially along the casing, each electronic unit comprising(i) a communication unit configured to enable the electronic unit tocommunicate with another electronic unit or with a surface terminal,(ii) a power supply, and (iii) at least one of: (a) a detectorcomprising at least one sensor configured to sense a physical orchemical magnitude or (b) a signal processor, at least one of theelectronic units configured as a relay in which the communication unitcomprises a receiver configured to receive signals transmitted by one ormore surrounding electronic units and a transmitter configured totransmit signals received from the one or more surrounding electronicunits and transformed by the signal processor; and fastening the casingelements together end-to-end to form the casing.